1. Field of the Invention
The invention relates to a control apparatus and a control method for a stepped vehicular automatic transmission, and particularly relates to an improvement for preventing the occurrence of a shock while improving shift response.
2. Description of Related Art
A stepped automatic transmission that selectively establishes a plurality of gears based on the running state of a vehicle from a predetermined shift diagram is widely used in various vehicles. In the automatic transmission described above, there is proposed a technology in which a plurality of types of shifts are selectively executed in accordance with the depression amount of an accelerator pedal. For example, a shift control apparatus for an automatic transmission described in Japanese Patent Application Publication No. 2002-295663 (JP-2002-295663 A) corresponds to the technology. According to this technology, when the depression speed of the accelerator pedal is relatively high, it is determined that the shift is the one placing emphasis on a shift speed, and the hydraulic pressure of an engagement device is reduced relatively quickly and the swift shift is performed, while when the depression speed of the accelerator pedal is relatively low, it is determined that the shift is the one placing emphasis on a shock and control in which the gradient of the hydraulic pressure of the engagement device is made gentle is performed, whereby it is possible to achieve shift feeling in response to the will of a driver.
However, in the related art described above, for example, when the shift placing emphasis on the shift speed is performed, there has been a problem that a reduction in output shaft torque is increased by quickly disengaging a disengagement-side engagement device to be disengaged in the shift. In particular, when a vehicle is running with a relatively large drive force, there has been a possibility that such reduction in output shaft torque leads to a redaction in drivability. This problem has been found out in the course of elaborate studies conducted by the inventors for the purpose of achieving both of excellent shift response and drivability in shift control of the automatic transmission.